Non-destructive testing and evaluation are well known and commonly used in various economic sectors of the world. Some examples of non-destructive testing and evaluation using gamma rays or ultrasound, for example, span the full range of industrial, biomedical, and research applications. Industrial applications involving hazardous materials are especially suitable for such testing and evaluation.
Inspection of pipes, carrying hazardous fluids or located in a hazardous environment, for signs of corrosion and/or erosion is one industrial application which is widely embraced by many companies. For example, pipes on nuclear submarines are regularly subjected to inspection for an early detection of corrosion and erosion. Radiographs of virtually every pipe in a nuclear submarine are obtained on a regular basis and examined by trained personnel. When a radiograph of a pipe shows some dark spots or shadows, signifying possible scattering or absorption of the incident X-rays as opposed to those transmitted through the pipe, it is a sign of possible corrosion or erosion in the pipe.
Obviously, replacing a pipe is not economically feasible even if possible corrosion or erosion is detected, because the extent of damage to the pipe may be negligible without posing any significant danger. The damaged pipe may be quite safe still fully conforming to the standards determined to be acceptable under particular conditions. In many situations, the damaged pipe may safely operate for a long period of time after the detection of the corrosion or erosion if the wall is still sufficiently thick. It is therefore apparent that the depth of the corrosion or, alternatively, the remaining wall thickness of the pipe is critically important and must be determined with high precision when the radiograph of the pipe reveals some signs of corrosion in certain spots.
Currently, after taking a radiograph, the area of the pipe showing corrosion is further inspected using ultrasound echo probes, for example, to more precisely determine the remaining wall thickness. This entails carrying an ultrasound equipment onto the submarine and preparing the area of the pipe for an ultrasound image. If the image shows that the corroded pipe does not require any repair or replacement, this procedure must be repeated at the next scheduled inspection. The pipe is thus closely monitored during the scheduled periodic inspections until it is determined that the corrosion or erosion poses a sufficient threat to the proper operation of the pipe.
It is apparent that the above procedure to determine the exact depth of corrosion or erosion has several significant drawbacks. First, the additional step of an ultrasound imaging is cumbersome and poses inconvenience to the inspecting personnel, including preparing the site again for inspection and carrying additional equipment thereto. Second, if facility is radioactive as is the case with a nuclear submarine, the inspecting personnel is subjected to the additional radiation exposure. Third, the ultrasonic measurements are not sufficiently accurate to provide the precise extent of the pipe corrosion.
Therefore, a need in the field of non-destructive testing and evaluation exists for a method and apparatus for pipe inspection that overcomes the above disadvantages.